The XAllocColor
function allocates a read-only colormap entry corresponding to the closest
RGB value supported by the hardware. XAllocColor returns the pixel value
of the color closest to the specified RGB elements supported by the hardware
and returns the RGB value actually used. The corresponding colormap cell
is read-only. In addition, XAllocColor returns nonzero if it succeeded
or zero if it failed. Multiple clients that request the same effective
RGB value can be assigned the same read-only entry, thus allowing entries
to be shared. When the last client deallocates a shared cell, it is deallocated.
XAllocColor does not use or affect the flags in the XColor structure.

XAllocColor can generate a BadColor error.

The XAllocNamedColor function
looks up the named color with respect to the screen that is associated
with the specified colormap. It returns both the exact database definition
and the closest color supported by the screen. The allocated color cell
is read-only. The pixel value is returned in screen_def_return. If the color
name is not in the Host Portable Character Encoding, the result is implementation-dependent.
Use of uppercase or lowercase does not matter. If screen_def_return and
exact_def_return point to the same structure, the pixel field will be set
correctly, but the color values are undefined. XAllocNamedColor returns
nonzero if a cell is allocated; otherwise, it returns zero.

XAllocNamedColor
can generate a BadColor error.

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The XAllocColorCells
function allocates read/write color cells. The number of colors must be
positive and the number of planes nonnegative, or a BadValue error results.
If ncolors and nplanes are requested, then ncolors pixels and nplane plane
masks are returned. No mask will have any bits set to 1 in common with any
other mask or with any of the pixels. By ORing together each pixel with
zero or more masks, ncolors * %2 sup nplanes% distinct pixels can be produced.
All of these are allocated writable by the request. For GrayScale or
PseudoColor, each mask has exactly one bit set to 1. For DirectColor,
each has exactly three bits set to 1. If contig is True and if all
masks are ORed together, a single contiguous set of bits set to 1 will
be formed for GrayScale or PseudoColor and three contiguous sets
of bits set to 1 (one within each pixel subfield) for DirectColor. The
RGB values of the allocated entries are undefined. XAllocColorCells returns
nonzero if it succeeded or zero if it failed.

XAllocColorCells can generate
BadColor and BadValue errors.

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The specified ncolors
must be positive; and nreds, ngreens, and nblues must be nonnegative,
or a BadValue error results. If ncolors colors, nreds reds, ngreens greens,
and nblues blues are requested, ncolors pixels are returned; and the masks
have nreds, ngreens, and nblues bits set to 1, respectively. If contig
is True, each mask will have a contiguous set of bits set to 1. No mask
will have any bits set to 1 in common with any other mask or with any of
the pixels. For DirectColor, each mask will lie within the corresponding
pixel subfield. By ORing together subsets of masks with each pixel value,
ncolors * %2 sup (nreds+ngreens+nblues)% distinct pixel values can be
produced. All of these are allocated by the request. However, in the colormap,
there are only ncolors * %2 sup nreds% independent red entries, ncolors
* %2 sup ngreens% independent green entries, and ncolors * %2 sup nblues%
independent blue entries. This is true even for PseudoColor. When the
colormap entry of a pixel value is changed (using XStoreColors, XStoreColor,
or XStoreNamedColor), the pixel is decomposed according to the masks,
and the corresponding independent entries are updated. XAllocColorPlanes
returns nonzero if it succeeded or zero if it failed.

XAllocColorPlanes
can generate BadColor and BadValue errors.

The XFreeColors function
frees the cells represented by pixels whose values are in the pixels array.
The planes argument should not have any bits set to 1 in common with any
of the pixels. The set of all pixels is produced by ORing together subsets
of the planes argument with the pixels. The request frees all of these pixels
that were allocated by the client (using XAllocColor, XAllocNamedColor,
XAllocColorCells, and XAllocColorPlanes). Note that freeing an individual
pixel obtained from XAllocColorPlanes may not actually allow it to be
reused until all of its related pixels are also freed. Similarly, a read-only
entry is not actually freed until it has been freed by all clients, and
if a client allocates the same read-only entry multiple times, it must free
the entry that many times before the entry is actually freed.

All specified
pixels that are allocated by the client in the colormap are freed, even
if one or more pixels produce an error. If a specified pixel is not a valid
index into the colormap, a BadValue error results. If a specified pixel
is not allocated by the client (that is, is unallocated or is only allocated
by another client) or if the colormap was created with all entries writable
(by passing AllocAll to XCreateColormap), a BadAccess error results.
If more than one pixel is in error, the one that gets reported is arbitrary.

A client attempted to free a color map entry that
it did not already allocate.

BadAccess

A client attempted to store into
a read-only color map entry.

BadColor

A value for a Colormap argument does
not name a defined Colormap.

BadValue

Some numeric value falls outside
the range of values accepted by the request. Unless a specific range is
specified for an argument, the full range defined by the argument's type
is accepted. Any argument defined as a set of alternatives can generate
this error.